The NTSB has released an Aviation Investigation Report (AIR-22-04) around six accidents of the Cirrus SR22T model and has advised Cirrus Aircraft to conduct a “functional hazard assessment” (FHA) for a closer look at risks surrounding fuel flow management during takeoff and climb phases of flight.
On normally aspirated Cirrus SR22 models, the two-sided fuel pump switch features a PRIME function that is momentary in operation; release and it stops. But on the turbocharged SR22T model, the PRIME side of the switch is continuous and provides a HIGH BOOST function used to clear vapor locked fuel lines, typically above 18,000 feet. In both models, the switch is located on the center console by the throttle and is physically “unguarded,” that is, has an exposed and directly operable switch, instead of one with a guarding mechanism, like a cover.
The Board studied six SR22T accidents caused by excessive fuel flow and examined data from recoverable data modules (RDM) in the Garmin G1000 avionics. They documented an “excessively high fuel flow” condition, ranging from 42.2 to 50.1 gallons per hour (GPH) just before the engine lost power in each case. The correct max-power fuel flow for takeoff and clim is 41 GPH. However, only in two of the six accidents could the Board confirm the pump switch was set to HIGH BOOST, causing the excessive flow condition.
The Report acknowledges Cirrus took “several steps” in 2018 to address this issue, like the addition of a software lockout for the HIGH BOOST function below 10,000 feet, and a CAS alert for the pilot. Unfortunately, a software bug prevented the new lockout from being completely reliable and forced another update in 2019.
The Report asserts, “!it is unclear whether the software updates will adequately address all excessive fuel conditions during takeoff,” and that, “Cirrus did not consider pilot performance related to recognition, reaction time, and recovery from an engine power loss at low altitude.” Finally, the NTSB believes there may be “!additional potential causes for excessive fuel-flow related engine failures that have not yet been identified,” and advises Cirrus to be proactive with the issue.
